1. Field of the Invention
The present invention relates generally to a method for storing vinyl ester resin or unsaturated polyester resin and more particularly, to a method for extending the shelf life of the vinyl ester resin or the unsaturated polyester resin.
2. Description of the Related Art
Carbon-carbon unsaturated double bonds of the molecular structure of vinyl ester resin or unsaturated polyester resin are very easily affected by the impurities contained in the vinyl ester resin or the unsaturated polyester resin or the ambient temperature in the stage of storing the vinyl ester resin or the unsaturated polyester resin, resulting in that the carbon-carbon unsaturated double bonds break to produce free radicals which tend to conduct a chain-reaction polymerization. The higher the ambient temperature increases or the more the storage amount of the vinyl ester resin or the unsaturated polyester resin increases, the more the chain reaction of the self-polymerization through the carbon-carbon unsaturated double bonds occurs easily and extensively. As a result, a gelation phenomenon of the vinyl ester resin or the unsaturated polyester resin caused by the foregoing self-polymerization reaction occurs during transportation or general storage, resulting in a monetary loss due to deterioration of the workability of the vinyl ester resin or the unsaturated polyester resin.
In a conventional method for resolving the aforesaid problem, a free radical inhibitor is added to the vinyl ester resin or the unsaturated polyester resin to minimize the self-polymerization reaction through the carbon-carbon unsaturated double bonds, so as to extend the shelf life of the vinyl ester resin or the unsaturated polyester resin. However, the addition of the aforesaid inhibitor will reduce the reactivity of the vinyl ester resin or the unsaturated polyester resin, thus causing poor problems, for example, the processing time of the vinyl ester resin or the unsaturated polyester resin is increased, such that the whole time for manufacturing a product from the vinyl ester resin or the unsaturated polyester resin is increased, or the vinyl ester resin or the unsaturated polyester resin cannot be cured completely, such that the strength of a product manufactured therefrom fails to satisfy the standard value, undesirably increasing the defective rate. Further, if the additive amount of the inhibitor is excessive, the color of cured vinyl ester resin or cured unsaturated polyester resin becomes darkened, thus the color of a product manufactured therefrom will be darkened, undesirably degrading the appearance of the product.
In another conventional method for resolving the above-mentioned problem, the vinyl ester resin or the unsaturated polyester resin is stored in a freezer during transportation or general storage to reduce the activation energy of the carbon-carbon unsaturated double bonds of the vinyl ester resin or the unsaturated polyester resin, thereby extending the shelf life of the vinyl ester resin or the unsaturated polyester resin. However, the cost for performing the foregoing prior art method is too high, thus undesirably increasing the price of the vinyl ester resin or the unsaturated polyester resin.